Estrous cycle characteristics and response to estrus synchronization in mammoth asses (Equus asinus americanus)

Breeding records from a herd of mammoth asses (Equus asinus americanus) mai ntained on pasture in southeast Texas from 1990 to 1998 were reviewed. Jenn ies were pasture or hand mated, and estrus was either observed while the je nnies were on pasture or when exposed to a jack after being penned. Eighty- one estrus periods and 43 diestrus intervals were recorded in 33 jennies ov er 4 seasons of the year (January-March, April-June, July-September, and Oc tober-December). Estrous cycle length and the duration of estrus were simil ar among seasons. Over all seasons, estrous cycle length was 23.3 +/- 2.6 d , duration of estrus was 5.9 +/- 2.1 d, and diestrus length was 17.4 +/- 2. 6 d (mean +/- SD). During these same 9 yr, 58 injections of PGF(2)alpha (5 mg, im) were administered to 38 jennies without regard to stage of estrous cycle. Seventy-six percent (44/58) of the jennies showed signs of estrus af ter PGF(2)alpha treatment, with an interval to estrus of 4.4 +/- 1.6 d and a duration of estrus of 5.6 +/- 1.7 d. Two estrus synchronization schemes w ere also assessed. Trial 1 was performed in October to November 1996, and T rial 2 was performed in February to March 1998. In Trial 1 (Croup PE+PGF, n = 10), each jenny was injected intramuscularly once daily for 10 d with 15 0 mg progesterone and 10 mg estradiol-17 beta in sesame oil, and PGF(2)alph a (10 mg) was injected intramuscularly on the last day of treatment. In Tri al 2 (Group PGF-2X, n = 11), each jenny was injected intramuscularly twice, 16 d apart, with 10 mg PGF(2)alpha. All Group PE+PGF jennies responded to treatment. One jenny in Group PGF-2X did not respond to either injection of PGF(2)alpha, while 2 jennies responded to the first but not the second PGF (2)alpha injection (8 of 11 jennies returned to estrus and ovulated after t he second PGF(2)alpha injection). Duration of estrus was 6.8 +/- 1.9 d for Group PE + PGF and 7.1 +/- 1.8 d for Group PGF-2X jennies. Interval to estr us and interval to ovulation following the last treatment were 9.0 +/- 0.9 d and 14.5 +/- 1.7 d, respectively, in Group PE+PGF jennies, and 4.5 +/- 0. 9 d and 10.4 +/- 1.8 d, respectively, for Group PGF-2X jennies. In summary, estrous cycle characteristics of mammoth asses are similar to those report ed for standard jennies, and estrus synchronization schemes used in horses are effective in mammoth asses. (C) 1999 by Elsevier Science Inc.